1. Field of the Invention
This invention relates to a magnetic tape cassette.
2. Description of the Prior Art
As shown in FIG. 3, in a magnetic tape cassette 1, a magnetic tape 3 wound around a reel 2 is run along a predetermined path under the guidance of guide members and the like and taken up around a take-up reel 4 during recording or reproduction.
Generally the tape running path is complicated in order to improve running stability of the tape 3 and to apply a proper tension to the tape 3. For example, the tape 3 is run along an S-shaped path near the take-up reel 4 under the guidance of a guide roller 5 and guide pin 6 mounted on the lower cassette half 7 to be taken up around the take-up reel 4 in a predetermined tension.
When assembling such a magnetic tape cassette 1, the tape 3 must be inserted into such a complicated tape running path. The tape insertion is generally effected in the following way. The reels 2 and 4 are held in a relative position conforming to the relative position in the lower cassette half 7, and the tape 3 is drawn out and held in a shape conforming to the running path in the cassette by a plurality of forming pins. In this state, the reels 2 and 4 and the tape 3 are lowered and incorporated in the lower casing half 7 which opens upward.
In the tape insertion, insertion of the tape 3 into the S-shaped part of the running path defined by said guide roller 5 and the guide pin 6 can be disturbed by a wall portion 7b of the lower casing half 7 surrounding a locating hole 7a near the S-shaped part, particularly a projection 7c of the wall portion 7b projecting toward the S-shaped part which can interfere with the forming pins or the tape. In order successfully to insert the tape 3 into the S-shaped part of the tape running path without interference of the wall portion 7b or the projection 7c with the tape or the forming pins, there have been made various contrivances on the shape of the forming pins, position of the same and the like.
In one of the contrivances, a pair of forming pins 8 and 9 which are positioned as shown in FIG. 4 relative to the guide roller 5 and the guide pin 6 are used. The forming pin 9 has an arcuate cross-section extending along the peripheral surface of the guide pin 6. With this arrangement, the tape 3 is made to extend arcuately along the peripheral surface of the guide pin 6, whereby interference of the tape 3 with the projection 7c is prevented.
In another of the contrivances, a small diameter forming pin 9a is used as shown in FIG. 5 in place of the arcuate forming pin 9 shown in FIG. 4. The small diameter forming pin 9a is placed between the guide members 5 and 6 and the projection 7c to bend the tape 3 at the forming pin 9a, thereby preventing interference of the tape 3 with the projection 7c when inserting the tape 3 between the guide members 5 and 6.
However, these forming pins 9 and 9a are disadvantageous in that they are very low in strength, and accordingly, they are apt to be bent by accident during adjustment of the tape insertion system and can be readily deformed by light external force.
Further, since the tape 3 is wrapped around the forming pin 9 or 9a after the forming pin 8, the level at which the tape 3 is wound around the forming pin 9 or 9a is apt to be affected by the verticality of the forming pin 8 and can be vertically deviated from the correct level defined by the flange surface of the take-up reel 4. When the level of the tape 3 is deviated downward, the lower edge portion of the tape 3 can project downward from the lower end of the forming pin 9 or 9a, and the tape 3 can be damaged by the lower end of the forming pin upon application of tape tension. This may be avoided by elongating the forming pin. However, in the arrangement shown in FIG. 4 or 5, the length of the forming pin is limited since the forming pin is moved toward the lower casing half 7 when incorporating the reels 2 and 4 and the tape 3 into the casing half 7, and cannot be sufficiently long to prevent damage on the tape 3.
The problems described above may be overcome by the use of a forming pin 9b having a larger diameter and a larger length and by arranging the forming pin 9b to move up and down with respect to the lower casing half 7 outside the lower casing half 7 as shown in FIG. 6. However, since the tape 3 must be drawn outside the lower casing half 7 in this case, the tape 3 must be arranged to extend at an angle counterclockwise (as seen in FIG. 6) to the direction perpendicular to the line joining the centers of the guide members 5 and 6 in order to avoid interference with the projection 7c. This gives rise to another problem that the forming pin 8 must be positioned nearer to the guide member 5 and accordingly must be small in diameter, which weakens the forming pin 8. Further, even if the problem of the strength of the forming pin 8 may be overcome, the tape 3 runs close to the projection 7c and the guide members 5 and 6 and accordingly fluctuation in positioning of the tape by the tape insertion system or fluctuation in dimensions of the lower casing half 7 can cause interference of the tape 3 with the projection 7c, or the guide member 5 or 6.
There has been a lower casing half 7' having a wall portion 7'b provided with no projection as shown in FIG. 7. In this case, by positioning forming pins 8' and 9' so that the tape 3 extends therebetween in perpendicular to the line joining the centers of the guide members 5 and 6 and by positioning the forming pin 9' inside the lower casing half 7', the problem of interference of the tape 3 with the guide member 5 or 6 or the wall portion 7'b can be solved. However, the problem of the length of the forming pin 9' still remains. When intending to solve the problem of the length of the forming pin 9' by positioning the forming pin 9' outside the lower casing half 7' as shown by the chain line in FIG. 7, the problem of interference of the tape 3 with the wall portion 7'b again arises. Further, if the tape 3 is counterclockwise inclined in order to prevent interference of the tape 3 with the wall portion 7'b, the problem of the diameter of the forming pin 8' or interference of the tape 3 with the guide member 5 or 6 arises.